Denitrification Oxygen Credit Calculator
Every milligram of nitrate reduced to nitrogen gas pays back oxygen to the process. Enter flow and nitrate-N denitrified to credit it against your aeration demand.
Denitrification Oxygen Credit
| Item | Value |
|---|
How the calculation works
Formulas
O2 credit (lb/day) = 2.86 × 8.34 × flow (MGD) × NO3-N denitrified (mg/L)
Nitrate carries chemically bound oxygen: reducing 1 mg of NO3-N to N2 gas releases the equivalent of 2.86 mg of O2. Subtract this credit from the total oxygen requirement when sizing or trimming aeration.
O2 credit (lb/day) = 2.86 × 8.34 × flow (MGD) × NO3-N denitrified (mg/L)
Nitrate carries chemically bound oxygen: reducing 1 mg of NO3-N to N2 gas releases the equivalent of 2.86 mg of O2. Subtract this credit from the total oxygen requirement when sizing or trimming aeration.
| Nitrogen step | Oxygen equivalent |
|---|---|
| Nitrification demand (NH4-N → NO3-N) | 4.57 mg O2 / mg N |
| Denitrification credit (NO3-N → N2) | 2.86 mg O2 / mg N |
| Net for full nitrification + denitrification | 1.71 mg O2 / mg N |
Notes & limitations
The 2.86 mg O2 per mg NO3-N factor is the theoretical COD equivalent of nitrate (Metcalf & Eddy, Wastewater Engineering). The 4.57 nitrification demand is the matching theoretical value.
- Only nitrate fully reduced to nitrogen gas earns the credit. Nitrate that leaves in the effluent or WAS earns nothing.
- Subtract the credit from the oxygen requirement computed for carbonaceous BOD plus nitrification — it directly reduces blower demand in BNR plants.
- The credit assumes denitrification goes to completion (N2). Significant nitrite accumulation changes the stoichiometry.
- Estimate NO3-N denitrified from an influent/effluent nitrogen balance or from recycle flows and zone concentrations, not from a single grab.
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